arXiv subjects

C. Giusti

Publications and source records attributed to C. Giusti.

At least 55 records · Page 3Linked to original sources

arXiv2004

Antisymmetrized Green's function approach to $(e,e')$ reactions with a realistic nuclear density

A completely antisymmetrized Green's function approach to the inclusive quasielastic $(e,e')$ scattering, including a realistic one-body density, is presented. The single particle Green's function is expanded in terms of the eigenfunctions of the nonhermitian optical potential. This allows one to treat final state interactions consistently in the inclusive and in the exclusive reactions. Nuclear correlations are included in the one-body density. Numerical results for the response functions of $^{16}$O and $^{40}$Ca are presented and discussed.

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arXiv2004

Effects of nuclear correlations on the $^{16}$O$(e,e'pN)$ reactions to discrete final states

Calculations of the $^{16}$O$(e,e'pN)$ cross sections to the ground state and first excited levels of the $^{14}$C and $^{14}$N nuclei are presented. The effects of nuclear fragmentation have been obtained in a self-consistent approach and are accounted for in the determination of the two-nucleon removal amplitudes. The Hilbert space is partitioned in order to compute the contribution of both long- and short-range effects in a separate way. Both the two-proton and the proton-neutron emission cross sections have been computed within the same models for the reaction mechanism and the contribution from nuclear structure, with the aim of better comparing the differences between the two physical processes. The $^{16}$O$(e,e'pp)$ reaction is found to be sensitive to short-range correlations, in agreement with previous results. The $^{16}$O$(e,e'pn)$ cross section to $1^+$ final states is dominated by the $Δ$ current and tensor correlations. For both reactions, the interplay between collective (long-range) effects and short-range and tensor correlations plays an important role. This suggests that the selectivity of $(e,e'pN)$ reactions to the final state can be used to probe correlations also beyond short-range effects.

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arXiv2004

Jastrow Two-nucleon Overlap Functions and Cross Sections of $^{16}$O$(e,e^{\prime}NN)^{14}$C Reactions

Using the relationship between the two-particle overlap functions (TOF's) and the two-body density matrix (TDM), the TOF's for $^{16}$O$(e,e^{\prime}pp)^{14}$C reaction are calculated on the basis of TDM obtained with a Jastrow-type approach. The main contributions of the removal of $^1S$ and $^3P$ $pp$-pairs from $^{16}$O are taken into account in the calculations of the cross sections of the $^{16}$O$(e,e^{\prime}pp)^{14}$C reaction using the Jastrow TOF's. The contributions of the one-body and two-body delta currents are considered. The results are compared with the calculations using TOF's from other approaches.

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arXiv2003

Structural Studies of Many-Body Systems and (e,e'p) Reaction Cross Sections

Studies of one-body density matrices (ODM) are performed in various correlation methods, such as the Jastrow method, the correlated basis function method, the Green's function method and the generator coordinate method aiming to extract the absolute spectroscopic factors and overlap functions (OF) for one-nucleon removal reactions from the ODM of the target nucleus. The advantage of this method is that it avoids the complicated task of calculating the total nuclear spectral function. The procedure for extracting bound-state OF's has been applied to make calculations of the cross sections of the $(e,e^{\prime}p)$ reaction on the closed-shell nuclei $^{16}$O and $^{40}$Ca as well as on the open-shell nucleus $^{32}$S consistently (using the same OF's) with the cross sections of $(p,d)$ and $(γ,p)$ reactions on the same nuclei. The analyses of the reaction cross sections and the spectroscopic factors and the comparison with the experimental data show the particular importance of these OF's, since they contain effects of nucleon correlations (short-range and/or long-range) which are accounted for to different extent in the theoretical methods considered.

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arXiv2003

Green's Function Approach to Inclusive Electron Scattering

A Green's function approach to the inclusive quasielastic ($e,e'$) scattering is presented. The components of the nuclear response are written in terms of the single-particle optical model Green's function. The explicit calculation of the Green's function can be avoided by its spectral representation, which is based on a biorthogonal expansion in terms of the eigenfunctions of the non-Hermitian optical potential and of its Hermitian conjugate. This allows one to treat final state interactions consistently in the inclusive ($e,e'$) and in the exclusive ($e,e'N$) reactions. Numerical results for the longitudinal and transverse response functions obtained in a nonrelativistic and in a relativistic framework are presented and discussed also in comparison with data.

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arXiv2003

The NN-final-state-interaction in two-nucleon-knockout reactions

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arXiv2003

NN correlations and final-state interactions in (e,e'NN) reactions

After a brief overview of relevant studies on one-nucleon knockout showing the importance of quantitatively understanding the origin of the quenched spectroscopic factors extracted from data, attention is focussed on two-nucleon emission as a suitable tool to investigate nucleon-nucleon correlations inside complex nuclei. In particular, direct (e,e$'$pp) and (e,e$'$pn) reactions are discussed, and the role of final-state interactions is studied. The influence of the mutual interaction between the two outgoing nucleons is shown to depend on the kinematics and on the type of the considered reaction.

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arXiv2003

NN final-state interaction in two-nucleon knockout from $^{16}O$

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in electro- and photoinduced two-nucleon knockout from $^{16}O$ has been investigated perturbatively. It turns out that the effect of NN-FSI depends on the kinematics and on the type of reaction considered. The effect is generally larger in pp- than in pn-knockout and in electron induced than in photoinduced reactions. In superparallel kinematics NN-FSI leads in the $(e,e'pp)$ channel to a strong increase of the cross section, that is mainly due to a strong enhancement of the $Δ$-current contribution. In pn-emission, however, this effect is partially cancelled by a destructive interference with the seagull current. For photoreactions NN-FSI is considerably reduced in superparallel kinematics and can be practically negligible in specific kinematics.

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arXiv2002

On the NN-final-state-interaction in the $^{16}{O}(e,e' pp)$ reaction

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in the $^{16}{O}(e,e' pp)$ reaction has been investigated. Results for various kinematics are discussed. In general, the effect of NN-FSI depends on kinematics and the chosen final state in the excitation spectrum of $^{14}{C}$.

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arXiv2002

Meson exchange currents in electromagnetic one-nucleon emission

The role of meson exchange currents (MEC) in electron- and photon-induced one-nucleon emission processes is studied in a nonrelativistic model including correlations and final state interactions. The nuclear current is the sum of a one-body and of a two-body part. The two-body current includes pion seagull, pion-in-flight and the isobar current contributions. Numerical results are presented for the exclusive 16O(e,e'p)15N and 16O(γ,p)15N reactions. MEC effects are in general rather small in (e,e'p), while in (γ,p) they are always large and important to obtain a consistent description of (e,e'p) and (γ,p) data, with the same spectroscopic factors. The calculated (γ,p) cross sections are sensitive to short-range correlations at high values of the recoil momentum, where MEC effects are larger and overwhelm the contribution of correlations.

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arXiv2002

Jastrow-type calculations of one-nucleon removal reactions on open $s$-$d$ shell nuclei

Single-particle overlap functions and spectroscopic factors are calculated on the basis of Jastrow-type one-body density matrices of open-shell nuclei constructed by using a factor cluster expansion. The calculations use the relationship between the overlap functions corresponding to bound states of the $(A-1)$-particle system and the one-body density matrix for the ground state of the $A$-particle system. In this work we extend our previous analyses of reactions on closed-shell nuclei by using the resulting overlap functions for the description of the cross sections of $(p,d)$ reactions on the open $s$-$d$ shell nuclei $^{24}$Mg, $^{28}$Si and $^{32}$S and of $^{32}$S$(e,e^{\prime}p)$ reaction. The relative role of both shell structure and short-range correlations incorporated in the correlation approach on the spectroscopic factors and the reaction cross sections is pointed out.

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arXiv2002

Two-proton overlap functions in the Jastrow correlation method and cross section of the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction

Using the relationship between the two-particle overlap functions (TOF's) and the two-body density matrix (TDM), the TOF's for the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction are calculated on the basis of a TDM obtained within the Jastrow correlation method. The main contributions of the removal of $^1S_0$ and $^3P_1$ $pp$ pairs from $^{16}$O are considered in the calculation of the cross section of the $^{16}$O$(e,e^{\prime}pp)^{14}$C$_{\rm g.s.}$ reaction using the Jastrow TOF's which include short-range correlations (SRC). The results are compared with the cross sections calculated with different theoretical treatments of the TOF's.

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arXiv2001

Nucleon-Nucleon Correlations in Electromagnetically Induced Knockout Reactions

The attempts to investigate correlations in electromagnetically induced one- and two-nucleon knockout are reviewed. The theoretical framework for cross section calculations is outlined and some results are presented for the exclusive $^{16}$O($e,e'p)^{15}$N and $^{16}$O($e,e'pp)^{14}$C reactions. For the ($e,e'p$) reaction attention is focussed on extracting the spectroscopic factors. For the ($e,e'pp$) reaction the possibility of obtaining direct and clear information on short-range correlations is discussed.

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arXiv2001

Polarization observables in (${\vec γ},{\vec N}N$) reactions

The formalism of (${\vec γ},{\vec N}N$) reactions is given where the incident photon is polarized and the outgoing nucleon polarization is detected. Sixteen structure functions and fifteen polarization observables are found in the general case, while only eight structure functions and seven polarizations observables survive in coplanar kinematics. Numerical examples are presented for the $^{16}$O($γ,pn$) and $^{16}$O($γ,pp$) reactions. The transitions to the ground state of $^{14}$C and $^{14}$N are calculated in a model where realistic short-range and tensor correlations are taken into account for the $pn$ pair, while short-range and long-range correlations are included in a consistent way for $pp$ pairs. The effects of the one-body and two-body components of the nuclear current and the role of correlations in cross sections and polarizations are studied and discussed.

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arXiv2001

Relativistic corrections in (gamma,N) knockout reactions

We develop a fully relativistic DWIA model for photonuclear reactions using the relativistic mean field theory for the bound state and the Pauli reduction of the scattering state which is calculated from a relativistic optical potential. Results for the 12C(gamma,p) and 16O(gamma,p) differential cross sections and photon asymmetries are displayed in a photon energy range between 60 and 257 MeV, and compared with nonrelativistic DWIA calculations. The effects of the spinor distortion and of the effective momentum approximation for the scattering state are discussed. The sensitivity of the model to different prescriptions for the one-body current operator is investigated. The off-shell ambiguities are large in (gamma,p) calculations, and even larger in (gamma,n) knockout.

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arXiv2001

Polarization Observables in (${\vec e},e'{\vec N}N$) and (${\vec γ},{\vec N}N$) Reactions

Nucleon recoil polarization in electromagnetic reactions with two-nucleon emission is discussed for both (${\vec e},e'{\vec N}N$) and (${\vec γ},{\vec N}N$). Numerical results are given for exclusive two-nucleon knockout reactions from $^{16}$O in a theoretical model where final-state interactions, one-body and two-body currents, and the effect of correlations in the initial pair wave function are included.

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arXiv2001

Generator coordinate method calculations of one-nucleon removal reactions on $^{40}$Ca

An approach to the Generator Coordinate Method (GCM) using Skyrme-type effective forces and Woods-Saxon construction potential is applied to calculate the single-particle proton and neutron overlap functions in $^{40}$Ca. The relationship between the bound-state overlap functions and the one-body density matrix has been used. These overlap functions are applied to calculate the cross sections of one-nucleon removal reactions such as ($e,e'p$), ($γ,p$) and ($p,d$) on $^{40}$Ca on the same theoretical footing. A consistent description of data for the different reactions is achieved. The shapes of the experimental cross sections for transitions to the $3/2^{+}$ ground state and the first $1/2^{+}$ excited state of the residual nuclei are well reproduced by the overlap functions obtained within the GCM. An additional spectroscopic factor accounting for correlations not included in the overlap function must be applied to the calculated results to reproduce the size of the experimental cross sections.

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arXiv2001

Relativistic corrections in (e,e'p) knockout reactions

A consistent comparison between nonrelativistic and relativistic descriptions of the (e,e'p) reaction is presented. We use the nonrelativistic DWEEPY code and develop a fully relativistic model starting from the effective Pauli reduction for the scattering state and the relativistic mean field theory for the bound state. Results for the 16O(e,e'p) differential cross section and structure functions are compared in various kinematical conditions. A limit in energy of the validity of the nonrelativistic approach is established. The effects of spinor distortion and of the effective momentum approximation for the scattering state are discussed. A satisfactory agreement with data of differential cross sections, structure functions, and polarization observables is achieved.

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